PDZD8-mediated endoplasmic reticulum-mitochondria associations regulate sympathetic drive and blood pressure through the intervention of neuronal mitochondrial homeostasis in stress-induced hypertension.

Neuronal hyperexcitation in the rostral ventrolateral medulla (RVLM) drives heightened sympathetic nerve activity and contributes to the etiology of stress-induced hypertension (SIH). Maintenance of mitochondrial functions is central to neuronal homeostasis. PDZD8, an endoplasmic reticulum (ER) transmembrane protein, tethers ER to mitochondria. However, the mechanisms of PDZD8-mediated ER-mitochondria associations regulating neuronal mitochondrial functions and thereby mediating blood pressure (BP) in the RVLM of SIH were largely unknown. SIH rats were subjected to intermittent electric foot shocks plus noise for 2 h twice daily for 15 consecutive days. The underlying mechanisms of PDZD8 were investigated through in vitro experiments by using small interfering RNA and through in vivo experiments, such as intra-RVLM microinjection and Western blot analysis. The function of PDZD8 on BP regulation in the RVLM was determined in vivo via the intra-RVLM microinjection of adeno-associated virus (AAV)2-r-Pdzd8. We found that the c-Fos-positive RVLM tyrosine hydroxylase (TH) neurons, renal sympathetic nerve activity (RSNA), plasma norepinephrine (NE) level, BP, and heart rate (HR) were elevated in SIH rats. ER-mitochondria associations in RVLM neurons were significantly reduced in SIH rats. PDZD8 was mainly expressed in RVLM neurons, and mRNA and protein levels were markedly decreased in SIH rats. In N2a cells, PDZD8 knockdown disrupted ER-mitochondria associations and mitochondrial structure, decreased mitochondrial membrane potential (MMP) and respiratory metabolism, enhanced ROS levels, and reduced catalase (CAT) activity. These effects suggested that PDZD8 dysregulation induced mitochondrial malfunction. By contrast, PDZD8 upregulation in the RVLM of SIH rats could rescue neuronal mitochondrial function, thereby suppressing c-Fos expression in TH neurons and decreasing RSNA, plasma NE, BP, and HR. Our results indicated that the dysregulation of PDZD8-mediated ER-mitochondria associations led to the loss of the activity homeostasis of RVLM neurons by disrupting mitochondrial functions, thereby participating in the regulation of SIH pathology.

Microglia-derived TNF-α contributes to RVLM neuronal mitochondrial dysfunction via blocking the AMPK-Sirt3 pathway in stress-induced hypertension.

BACKGROUND: Neuroinflammation in the rostral ventrolateral medulla (RVLM) has been associated with the pathogenesis of stress-induced hypertension (SIH). Neuronal mitochondrial dysfunction is involved in many pathological and physiological processes. However, the impact of neuroinflammation on neuronal mitochondrial homeostasis and the involved signaling pathway in the RVLM during SIH are largely unknown. METHODS: The morphology and phenotype of microglia and the neuronal mitochondrial injury in vivo were analyzed by immunofluorescence, Western blot, RT-qPCR, transmission electron microscopy, and kit detection. The underlying mechanisms of microglia-derived tumor necrosis factor-α (TNF-α) on neuronal mitochondrial function were investigated through in vitro and in vivo experiments such as immunofluorescence and Western blot. The effect of TNF-α on blood pressure (BP) regulation was determined in vivo via intra-RVLM microinjection of TNF-α receptor antagonist R7050. RESULTS: The results demonstrated that BP, heart rate (HR), renal sympathetic nerve activity (RSNA), plasma norepinephrine (NE), and electroencephalogram (EEG) power increased in SIH rats. Furthermore, the branching complexity of microglia in the RVLM of SIH rats decreased and polarized into M1 phenotype, accompanied by upregulation of TNF-α. Increased neuronal mitochondria injury was observed in the RVLM of SIH rats. Mechanistically, Sirtuin 3 (Sirt3) and p-AMPK expression were markedly downregulated in both SIH rats and TNF-α-treated N2a cells. AMPK activator A769662 upregulated AMPK-Sirt3 signaling pathway and consequently reversed TNF-α-induced mitochondrial dysfunction. Microinjection of TNF-α receptor antagonist R7050 into the RVLM of SIH rats significantly inhibited the biological activities of TNF-α, increased p-AMPK and Sirt3 levels, and alleviated neuronal mitochondrial injury, thereby reducing c-FOS expression, RSNA, plasma NE, and BP. CONCLUSIONS: This study revealed that microglia-derived TNF-α in the RVLM impairs neuronal mitochondrial function in SIH possibly through inhibiting the AMPK-Sirt3 pathway. Therefore, microglia-derived TNF-α in the RVLM may be a possible therapeutic target for the intervention of SIH.

Autologous hematopoietic stem cell transplantation improves survival outcomes in peripheral T-cell lymphomas: a multicenter retrospective real-world study.

The aim of this study is to evaluate the survival benefit of consolidative autologous hematopoietic stem cell transplantation (ASCT) in patients with peripheral T-cell lymphomas (PTCL). In this retrospective study, the ASCT group underwent consolidative ASCT after first-line therapy at 14 transplantation centers in China between January 2001 and December 2019. Data were collected over the same time frame for the non-ASCT group from the database of lymphoma patient records at Peking University Cancer Hospital & Institute. A total of 120 and 317 patients were enrolled in the ASCT and non-ASCT groups, respectively, and their median ages were 43 years and 51 years, respectively. In the ASCT group, 101 patients had achieved complete remission (CR) and 19 patients had achieved partial remission at the time of ASCT. The median follow-up time was 40.2 months and 68 months, and the 3-year overall survival (OS) rate was 80.6% and 48.9% (p < 0.001) for the ASCT and non-ASCT groups, respectively. The beneficial effect of ASCT for OS remained even after propensity score-matched (PSM) analysis (81.6% vs 68.3%, p = 0.001). Among the 203 patients who were aged ≤ 65 years and achieved CR, ASCT conferred a significant survival benefit (3-year progression-free survival [PFS]: 67.4% vs 47.0%, p = 0.004; 3-year OS: 84.0% vs 74.1%, p = 0.010), and this was also maintained after PSM analysis (3-year PFS: 66.6% vs 48.4%, p = 0.042; 3-year OS: 84.8% vs 70.5%, p = 0.011). Consolidative ASCT improved the survival outcome of PTCL patients, even those who achieved CR after first-line therapy.

Do biological activities of selective histone deacetylase 6 (HDAC6) inhibitors rely on the modification of cap group?

Nowadays, significant progress has been made in the development of selective histone deacetylase 6 (HDAC6) inhibitors, exerting great potential in the treatment of various malignant tumors and neurodegenerative diseases. Previously, selective inhibitory activities of HDAC inhibitors were generally considered sensitive to the interactions between the Cap group and the binding site of HDAC6, and a large number of selective HDAC6 inhibitors have been designed and synthesized based on the strategy. However, some inhibitors without Cap group could also exhibit excellent potency and selective inhibition towards HDAC6, and in this study, BRD9757 and compound 8, as capless selective HDAC6 inhibitors, were selected as molecular probes to explore the difference of their binding interactions in HDAC1&6. Through the analysis of binding-free energies and conformational rearrangements after 1 µs molecular dynamics simulation, it could be learned that although the residues in the binding site remained highly consistent, the binding mechanisms of BRD9757 and compound 8 in HDAC1&6 were different, which will provide valuable hints for the discovery of novel selective HDAC6 inhibitors.

Kayadiol exerted anticancer effects through p53-mediated ferroptosis in NKTCL cells.

BACKGROUND: Extranodal natural killer/T cell lymphoma (NKTCL) is a highly aggressive type of non-Hodgkin lymphoma that facing the treatment challenges. Natural compounds are important sources for drug development because of their diverse biological and chemical properties, among which terpenoids have strong anticancer activities. METHODS: The human NK/T cell lymphoma cell line YT and peripheral blood lymphocytes isolated from NKTCL patients were treated with different concentrations of kayadiol. Then, the following experiments were performed: CCK-8 assay for cell viability, reactive oxygen species (ROS) and glutathione (GSH) assay and co-treatment with NAC, reduced GSH, or ferrostatin-1 for ferroptosis, the proteome profiling for elucidating signaling pathways, and western blot for the expression of p53, SCL7A11, and GPX4. siRNA and CRISPR/Cas9 plasmid for p53 knockout was designed and transfected into YT cells to evaluate the causal role of p53 in kayadiol-induced ferroptosis. The synergistic effect was evaluated by CCK8 assay after co-treatment of kayadiol with L-asparaginase or cisplatin. RESULTS: In this study, we found that kayadiol, a diterpenoid extracted from Torreya nucifera, exerted significant killing effect on NKTCL cells without killing the healthy lymphocytes. Subsequently, we observed that kayadiol treatment triggered significant ferroptosis events, including ROS accumulation and GSH depletion. ROS scavenger NAC, GSH, and ferroptosis inhibitor ferrostatin-1 (Fer-1) reversed kayadiol-induced cell death in NKTCL cells. Furthermore, kayadiol decreased the expression of SLC7A11 and GPX4, the negative regulatory proteins for ferroptosis. We then demonstrated that p53 was the key mediator of kayadiol-induced ferroptosis by SLC7A11/GPX4 axis through p53 knockout experiments. In addition, kayadiol exerted a synergistic effect with L-asparaginase and cisplatin in NKTCL cells. CONCLUSION: Taken together, our results suggested that the natural product kayadiol exerted anticancer effects through p53-mediated ferroptosis in NK/T cell lymphoma cells. Hence, it can serve as an effective alternative in the treatment of NK/T cell lymphoma, especially for patients exhibiting chemoresistance.

Unexpected favorable outcome to sintilimab monotherapy in a relapse pancreatic ductal adenocarcinoma patient with high tumor mutational burden: a case report.

The reason that immune checkpoint inhibitors have not been widely applied to pancreatic cancer treatment is probably because of low immunogenicity or dense stromal fibrosis. Recently, only pembrolizumab was recommended for DNA mismatch repair deficiency or high microsatellite instability by National Comprehensive Cancer Network guideline. Pancreatic ductal adenocarcinoma (PDAC) accounts for more than 90% of pancreatic cancer, with a poor overall survival rate, the value of immunotherapy for PDAC needs more research. Here, we report a 56-year-old man suffered from PDAC with liver metastasis after radical surgery. The next-generation sequencing result demonstrated that it had remarkably high tumor mutational burden (TMB) of 49.92 Muts/Mb and microsatellite stability. Sintilimab (anti-PD-1) monotherapy was continuously administrated after failure of combined chemotherapy in second line, achieving stable disease within 22 months and few immunotherapy-related adverse events. To our knowledge, this is the first time to report a good outcome achieving 22 months with progression-free survival after PDAC metastasis with monotherapy of sintilimab. TMB may serve as a potential efficacy-related predictor in PDAC patients with sintilimab and help physicians make optimum clinical strategy.

Comparison of resting-state spontaneous brain activity between treatment-naive schizophrenia and obsessive-compulsive disorder.

BACKGROUND: Schizophrenia (SZ) and obsessive-compulsive disorder (OCD) share many demographic characteristics and severity of clinical symptoms, genetic risk factors, pathophysiological underpinnings, and brain structure and function. However, the differences in the spontaneous brain activity patterns between the two diseases remain unclear. Here this study aimed to compare the features of intrinsic brain activity in treatment-naive participants with SZ and OCD and to explore the relationship between spontaneous brain activity and the severity of symptoms. METHODS: In this study, 22 treatment-naive participants with SZ, 27 treatment-naive participants with OCD, and sixty healthy controls (HC) underwent a resting-state functional magnetic resonance imaging (fMRI) scan. The amplitude of low-frequency fluctuation (ALFF), regional homogeneity (ReHo) and degree of centrality (DC) were performed to examine the intrinsic brain activity of participants. Additionally, the relationships among spontaneous brain activity, the severity of symptoms, and the duration of illness were explored in SZ and OCD groups. RESULTS: Compared with SZ group and HC group, participants with OCD had significantly higher ALFF in the right angular gyrus and the left middle frontal gyrus/precentral gyrus and significantly lower ALFF in the left superior temporal gyrus/insula/rolandic operculum and the left postcentral gyrus, while there was no significant difference in ALFF between SZ group and HC group. Compared with HC group, lower ALFF in the right supramarginal gyrus/inferior parietal lobule and lower DC in the right lingual gyrus/calcarine fissure and surrounding cortex of the two patient groups, higher ReHo in OCD group and lower ReHo in SZ group in the right angular gyrus/middle occipital gyrus brain region were documented in the present study. DC in SZ group was significantly higher than that in HC group in the right inferior parietal lobule/angular gyrus, while there were no significant DC differences between OCD group and HC group. In addition, ALFF in the left postcentral gyrus were positively correlated with positive subscale score (r = 0.588, P = 0.013) and general psychopathology subscale score (r = 0.488, P = 0.047) respectively on the Positive and Negative Syndrome Scale (PANSS) in SZ group. ALFF in the left superior temporal gyrus/insula/rolandic operculum of participants with OCD were positively correlated with compulsion subscale score (r = 0.463, P = 0.030) on the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS). The longer the illness duration in SZ group, the smaller the ALFF of the left superior temporal gyrus/insula/rolandic operculum (Rho = 0.-492, P = 0.020). The longer the illness duration in OCD group, the higher the ALFF of the right supramarginal gyrus/inferior parietal lobule (Rho = 0.392, P = 0.043) and the left postcentral gyrus (Rho = 0.385, P = 0.048), and the lower the DC of the right inferior parietal lobule/angular gyrus (Rho = - 0.518, P = 0.006). CONCLUSION: SZ and OCD show some similarities in spontaneous brain activity in parietal and occipital lobes, but exhibit different patterns of spontaneous brain activity in frontal, temporal, parietal, occipital, and insula brain regions, which might imply different underlying neurobiological mechanisms in the two diseases. Compared with OCD, SZ implicates more significant abnormalities in the functional connections among brain regions.

The Formation/Decomposition Equilibrium of LiH and its Contribution on Anode Failure in Practical Lithium Metal Batteries.

Discovering the underlying reason for Li anode failure is a critical step towards applications of lithium metal batteries (LMBs). In this work, we conduct deuterium-oxide (D2 O) titration experiments in a novel on-line gas analysis mass spectrometry (MS) system, to determine the content of metallic Li and lithium hydride (LiH) in cycled Li anodes disassembled from practical LiCoO2 /Li LMBs. The practical cell is comprised of ultrathin Li anode (50 µm), high loading LiCoO2 (17 mg cm-2 , 2.805 mAh cm-2 ) and different formulated electrolytes. Our results suggest that the amount of LiH accumulation is negatively correlated with cyclability of practical LMBs. More importantly, we reveal a temperature sensitive equilibrium (Li + 1/2 H2 ⇌ LiH) governing formation and decomposition process of LiH at Li anode. We believe that the unusual understanding provided by this study will draw forth more insightful efforts to realize efficient Li protection and the ultimate applications of "holy grail" LMBs.

Exonuclease III-assisted signal amplification strategy for sensitive fluorescence detection of polynucleotide kinase based on poly(thymine)-templated copper nanoparticles.

A sensitive and label-free fluorometric method has been developed for the determination of polynucleotide kinase (PNK) activity, by employing exonuclease III (Exo III)-assisted cyclic signal amplification and poly(thymine)-templated copper nanoparticles (polyT-CuNPs). In the presence of PNK, cDNA with 5'-hydroxyl termini was phosphorylated and then hybridized with tDNA to form the cDNA/tDNA duplex, which subsequently triggered the λ exonuclease cleavage reaction, eventually resulting in the release of tDNA. The released tDNA could unfold the hairpin structure of HP DNA to generate partially complementary duplex (tDNA/HP DNA), wherein the HP DNA possessed T-rich sequences (T30) and tDNA recognition sequence. With the help of Exo III digestion, the tDNA was able to initiate the cycle for the generation of T-rich sequences, the template for the formation of fluorescent CuNPs. Conversely, the cDNA could not be cleaved by λ exonuclease without PNK and individual HP DNA could not be hydrolyzed by Exo III. The T-rich sequence was caged in HP DNA, resulting in a weak fluorescence signal. Under optimized conditions, the fluorescence intensity was linearly correlated to a concentration range of 0.001 to 1 U mL-1 with a low detection limit of 2 × 10-4 U mL-1. Considering the intriguing analytical performance, this approach could be explored to screen T4 PNK inhibitors and hold promising applications in drug discovery and disease therapy.

Highly Stable Spherical Metallo-Capsule from a Branched Hexapodal Terpyridine and Its Self-Assembled Berry-type Nanostructure.

Discrete spherical metallo-organic capsules at the nanometer scale, especially those constructed from unique building blocks, have received significant attention recently because of their fascinating molecular aesthetics and potential applications due to their compact cavities. Here, the synthesis and characterization of a hexapodal, branched terpyridine ligand are presented along with the nearly quantitative self-assembly of the resulting tetrameric metallo-nanosphere. This metallo-nanosphere exhibited four quasi-triangular and six rhombus-like facets, all of which were made by the same hook-like bis-terpyridine. Collision-induced dissociation experiments were done to investigate overall stability. The metallo-architecture and host-guest chemistry were investigated with coronene and fully characterized by 1D and 2D NMR, ESI-MS, and transmission electron microscopy. Furthermore, this metallo-nanosphere was observed to hierarchically self-assemble into berry-type structures in an acetonitrile/methanol mixture, by virtue of counterion-mediated attractions. The functional molecular metallo-nanosphere presented here expands the reach of terpyridine coordination systems into molecular containers and other model systems.

Label-free detection of exonuclease III activity and its inhibition based on DNA hairpin probe.

In this paper, we have developed a label-free and rapid fluorescence assay for the detection of exonuclease III (exo III) activity via thioflavin T (ThT) as the G-quadruplex inducer. In this assay, a hairpin probe (HP) with a 5'-guanine-rich (G-rich) sequence is employed as the substrate for exo III. In the presence of exo III, HP can be digested at 3'-OH termini releasing 5'-G-rich sequence. Then, the 5'-G-rich sequence folds into a G-quadruplex, which can be recognized quickly by the ThT dye resulting in an increase in fluorescence emission. This strategy can detect exo III activity as low as 0.5 U/mL. This assay is simple and of low cost without the requirement of labeling with a fluorophore-quencher pair.

Fluorometric aptamer-based determination of ochratoxin A based on the use of graphene oxide and RNase H-aided amplification.

The authors describe a fluorometric assay for ochratoxin A (OTA) that is based on the use of graphene oxide and RNase H-aided amplification. On addition of OTA, cAPT is replaced from the APT/cAPT hybridization complex and then hybridizes with RNA labeled with a fluorophore at the 5'-end. Eventually, the fluorophore is released by RNase H cleavage. As the concentration of OTA increases, more cAPTs are displaced, this leading to fluorescence enhancement (best measured at excitation/emission wavelengths of 495/515 nm). This RNase H-assisted cycle response results in strong signal amplification. The limit of detection, calculated on the basis of a signal to noise ratio of 3, is 0.08 ng·mL-1. Response is linear in the 0.08-200 ng·mL-1 OTA concentration range. The method is highly selective for OTA over ochratoxin B and aflatoxin B1. It was applied to the determination of OTA in red wine samples spiked at levels of 1, 7, and 50 ng·mL-1, and the recoveries ranged from 90.9 to 112%. Graphical abstract Schematic of a novel fluorometric aptasensor for ochratoxin A based on the use of graphene oxide and RNase H-aided amplification.

Label-free colorimetric assay for T4 polynucleotide kinase/phosphatase activity and its inhibitors based on G-quadruplex/hemin DNAzyme.

Here we report a new approach for label-free colorimetric assay of T4 polynucleotide kinase/phosphatase (PNKP) activity based on G-quadruplex/hemin DNAzyme. In the presence of T4 PNKP, the DNA primer with a 3'-phosphate can be dephosphorylated into a 3'-hydroxyl and initiate a primer elongation reaction to open the hairpin probe, and leading to releasing the G-quartets. Under optimal conditions, the proposed method exhibited a considerable performance with a detection limit of 0.01 U/mL. Furthermore, the present assay can be used to study the potential T4 PNKP inhibitor screening, making it promise to be applied in the fields of drug discovery.

Label-free monitoring of DNA polymerase activity based on a thrombin-binding aptamer G-quadruplex.

We have developed a label-free assay for the detection of DNA polymerase activity based on a thrombin-binding aptamer (TBA) G-quadruplex. In the presence of DNA polymerase, the 3'-OH termini of the hairpin substrate are immediately elongated to replace the TBA, which can be recognized quickly by the ThT dye and results in an increase of fluorescence. This method is highly sensitive with a detection limit of 0.1 U/mL. It is simple and cost-effective without any requirement of labeling with a fluorophore-quencher pair. Furthermore, the proposed method can also be applied to analyze the inhibition of DNA polymerase, which clearly indicates that the proposed method can be applied for screening of potential DNA polymerase inhibitors.

An Exonuclease I-Based Quencher-Free Fluorescent Method Using DNA Hairpin Probes for Rapid Detection of MicroRNA.

MicroRNAs (miRNAs) act as biomarkers for the diagnosis of a variety of cancers. Since the currently used methods for miRNA detection have limitations, simple, sensitive, and cost-effective methods for the detection of miRNA are required. This work demonstrates a facile, quencher-free, fluorescence-based analytical method for cost-effective and sensitive detection of miRNA using a super 2-aminopurine (2-AP)-labeled hairpin probe (HP) and exonuclease I activity. Specifically, the fluorescence of 2-AP is strongly quenched when it is incorporated within DNA. In the presence of a target miRNA, HP attains an open conformation by hybridizing with the target miRNA to form a double-stranded structure with a protruding 3'-terminus. Next, the digestion of the protruding 3'-terminus is triggered by exonuclease I, during which 2-AP is released free in solution from the DNA, thereby increasing fluorescence. This method is highly sensitive, with a detection limit of 0.5 nM-10 times lower than a previously reported quencher-free fluorescence method. Furthermore, this method has potential applications in clinical diagnosis and biomedical research.

Quencher-free hairpin probes for real-time detection of T4 polynucleotide kinase activity.

Traditional methods of assaying polynucleotide kinase (PNK) activity are discontinuous, time-consuming, and laborious. Here we report a new quencher-free approach to real-time monitoring of PNK activity using a 2-aminopurine probe. When the 2-aminopurine probe was 5'-phosphorylated by PNK, it could be efficiently degraded by lambda exonuclease to release free 2-aminopurine molecules and generate a fluorescence signal. This method not only provides a universal approach to real-time monitoring of PNK activity, but also shows great potential for screening suitable inhibitor drugs for PNK.

Real-time monitoring of DNA methyltransferase activity using a hemimethylated smart probe.

A real-time assay for DNA methyltransferase (MTase) activity has been developed. A hemimethylated smart probe is used as the substrate for DNA MTase. Cleavage of the methylated product leads to separation of fluorophore from quencher, giving a proportional increase in fluorescence. The method permits real-time monitoring of DNA methylation process and makes it easy to characterize the activity of DNA MTase. It also has the potential to screen suitable inhibitor drugs for DNA MTase.

Label-free monitoring of DNA methyltransferase activity based on terminal deoxynucleotidyl transferase using a thioflavin T probe.

We have developed a new methodology for fluorescence turn-on detection of DNA methyltransferase (MTase) activity based on terminal deoxynucleotidyl transferase (TdT) using a thioflavin T probe. This method is highly selective and sensitive. The fluorescence intensity was direct proportion to Dam MTase concentration in the range from 0.1 to 8.0 U/mL with a detection limit of 0.1 U/mL. And because no labeling with a fluorophore-quencher pair was required, it is simple and low cost. We envision that our novel fluorescent detection method for Dam MTase activity could be applied as a useful tool in biomedical research.

Label-free molecular beacon for real-time monitoring of DNA polymerase activity.

Traditional methods for assaying DNA polymerase activity are discontinuous, time consuming, and laborious. Here, we report a new approach for label-free and real-time monitoring of DNA polymerase activity using a Thioflavin T (ThT) probe. In the presence of DNA polymerase, the DNA primer could be elongated through polymerase reaction to open MB1, leading to the release of the G-quartets. These then bind to ThT to form ThT/G-quadruplexes with an obvious fluorescence generation. It exhibits a satisfying detection result for the activity of DNA polymerase with a low detection limit of 0.05 unit/ml. In addition, no labeling with a fluorophore or a fluorophore-quencher pair is required; this method is fairly simple, fast, and low cost. Furthermore, the proposed method was also applied to assay the inhibition of DNA polymerase activity. This approach may offer potential applications in drug screening, clinical diagnostics, and some other related biomedical research.

Quencher-free fluorescence strategy for detection of DNA methyltransferase activity based on exonuclease III-assisted signal amplification.

This work demonstrates a novel method for DNA methyltransferase (MTase) activity detection with a quencher-free molecular beacon (MB) probe based on exonuclease (Exo) III-assisted signal amplification. In the presence of Dam MTase and DpnI endonuclease, the elaborately designed hairpin substrate (MB1) was cleaved into two parts (part A and part B). Exo III can then digest part A and release a single-stranded target of the 2-aminopurine-labeled MB (MB2). Subsequently, the MB2 can hybridize with its target to form a double-stranded structure with a protruding 3'-terminus and then trigger the digestion of MB2 by Exo III. During the digestion of MB2, the 2-aminopurine is separated from the DNA strands and released free in solution, inducing an increase of the fluorescent signal. Owing to the presence of a recessed 3'-terminus in the formed double-stranded DNA, Exo III-assisted recyclable cleavage of MB2 was achieved. Therefore, an amplified fluorescence signal was observed. Under the optimized conditions, Dam MTase can be detected in the range of 0.2-40 units/mL with a limit of detection of 0.2 units/mL and good selectivity. Furthermore, the present assay can be used for screening potential DNA MTase inhibitors. Graphical Abstract A quencher-free fluorescence assay for sensitive detection of DNA methyltransferase activity based on exonuclease III-assisted signal amplification is reported.